The present invention relates to a modem in a remote location which is capable of calling a central computer under varying operating conditions, and transferring data between the remote location and the central computer.
There are currently many consumer electronics systems which require that information be transmitted between the user""s location and a centrally located computer. One example is the direct satellite system (DSS) for television channel distribution. In the DSS system, when a user watches a pay-per-view television program, that information is transmitted back to a central computer via the user telephone line so the viewer can be properly charged for the viewing. For another example, there are currently television set top boxes which are capable of connecting to the internet, using the television screen as the display screen and the television remote as the keyboard. These set top boxes connect the computer in the set top box to the internet service provider (ISP) providing access to the internet via the user telephone line. Data is then sent to the ISP in response to user inputs, and corresponding data received from the ISP for display on the television screen, all under control of the set top box.
Telephone/modem data transfer links between cooperating computers are very well known. However, in the case of an internet set top box, the set top box is not part of a computer system under control of a computer operator. Instead, the user must be able to properly install the set top box with a minimum of technical knowledge.
Prior solutions for enabling a modem to operate automatically have addressed some of these problems. One such example is International Patent application No. PCT/US96/20514 filed Dec. 17, 1996 by Pitsch et al., and entitled, xe2x80x9cAN AUTOMATIC SUBSCRIBER CALLBACK SYSTEM.xe2x80x9d In Pitsch et al., an automatic modem is disclosed for a receiver in a DSS satellite television distribution system. This receiver gathers information, e.g. pay-per-view programs viewed by the subscriber, and transmits this information to a central computer, in an operation termed callback. Pitsch et al. addresses several of the problems of callback modems, which operate in an automatic manner.
First, the disclosed callback modem minimized interference with subscribers"" use of their telephone lines. Because a callback can occur automatically at a predetermined time, without any knowledge of whether the subscriber is using the telephone line, the disclosed callback mechanism ensured that such a callback could occur without interfering with the subscriber""s use of the telephone line, and without causing interference with, or degradation of, the subscriber""s phone operation. More specifically, the callback modem would not attempt a callback if a subscriber was using the telephone line, and immediately released the telephone line whenever the subscriber wanted access to the phone during a callback.
Second, the disclosed callback modem operated automatically with telephone central offices which may have abnormal interface behaviors. Some of the abnormal interfaces presented by central offices include: very short dial tones; pulse dial only; distorted dial tones; 60 Hz modulation on the dial tone; no dial tone; fast busy return tone; long delay before dial tone; and fluctuating telephone line current during telephone access and/or fluctuating current during off hook operation. The disclosed callback modem included a dial tone detector, line current monitor and access algorithm which detected such anomalies and adjusted the modem operation appropriately.
Third, the disclosed callback modem recognized that unknown distortions may be introduced by the telephone line connections between the callback modem and the central computer. Some such distortions were compensated by utilizing an adaptive equalizer, in a known manner. However, in some cases, the dynamic conditions of the telephone line, line loss conditions at the called modem location, and distortions presented by the modem coupling transformer were not correctable using an adaptive equalizer. The disclosed callback modem included power level output control, and possibly data verification and retransmission in severe cases, for compensating for such distortions.
The inventors have realized, however, that, while it is important that a modem be able to operate autonomously, as disclosed in Pitsch et al., it is also important that a user is able to easily connect and set up a modem xe2x80x9cout of the boxxe2x80x9d. This presents different problems. For example, when operation is attempted for the first time, the modem may not be properly connected to a telephone line, or the telephone line may be in use. It is also possible that the equipment may be installed in an office environment in which a dialing prefix is required to access an outside line. Further, it is possible for the telephone line to have the telephone service known as xe2x80x98call waitingxe2x80x99 installed. It is well known that this service can cause a disruption of an existing modem connection if a call is received for the subscriber telephone line while a data transfer call is in progress. It is desirable for an automatic modem to detect such conditions and operate properly in their presence.
In accordance with principles of the present invention, apparatus for automatically establishing a data connection includes a telephone line interface circuit coupled to a subscriber telephone line, and a modulator and demodulator circuit coupled to the telephone line interface circuit. A control circuit conditions the apparatus to establish a connection to the subscriber telephone line and comprises circuitry to determine whether a central office to which the subscriber telephone line is connected is a tone-dial central office or a pulse-dial-only central office, whether a dialing prefix is necessary to access the subscriber telephone line, and whether the call waiting feature is activated on the subscriber telephone line.